US2400751A - Safety high-voltage rectifier - Google Patents

Description

May 2l, 1946.

E. G. GAGE 2,400,751

I SAFETY HIGH VOLTAGE RECTIFIER Filed Fleb. 22, 1944 2 Sheets-Sheet 2 IN VEN TOR. EowA/QD 6. AGE

Patented May 21, 1946 SAFETY HIGH-VOLTAGE RECTIFIER Edward G. Gage,

Brooklyn, N. Y., assignor of two-thirds to Leon Ottlnger, New

York, N. Y.

" Application February 22, 1944, Serial No. 523.417

is claims. (ci. irs-ssa) The invention relates to high voltage rectiers, more especially thermionic rectiers such as are utilized'in connection with the operation of cathode ray tubes, luminescent or fluorescent tubes, X-ray apparatus, and similar devices utilizing voltages and currents of such magnitude as nor mally to be considered dangerous. These voltages constitute a hazard not only for those who may be required to service the apparatus, but also in some instances to those operating the same.

It has heretofore been thepractice to employ rectiers for such high voltages with but a single terminal for the anode and another for the cathode. Consequently if either were contacted by the human body While a dangerous power was on, a severe if not fatal shock was received through the "oody when the circuit was completed to ground or to the return lead of the supply source.

Tin my U. El. Patent Nos. 2,281,571 and 2,281,572 and my application for U. S. Letters Patent Serial No. 517,336, filed January '7, 1944, I have shown how sources of dangerous voltages, such as transformer and condenser circuits, may be made safe to handle. In the various systems disclosed therein a plurality ci.' rectiers is employed when the current required to operate the apparatus is more than can be safely contacted. By dividing the dangerous current into a number of separate paths, with individual rectiers in each path, the circuit paths are made safe by limiting the amount of current passing through each path to a value hy the insertion of resistors in these paths. The resistance value or such re sisters is always to be sulcicntly .low ier the op eration ci the apparatus when all'the paths are combined. Contacting any single path by the body results in receiving only the limited or safe current in that path, which is the result of a drop of voltage in the circuit path to a harmless value when contacted. Because of the asymmet-u ric properties of the rectifters, the currents in the unoontacted circuit portions are prevented from combining and returning through the body.

An object of the present invention is to combine these circuit paths' in a single rectifier element instead of employing a separate rectifier for each path. By this means the cost of the apparatus is greatly reduced and the entire system greatly simplified.

A further object is to provide a novel combined socket and Junction box for the rectiiier.

A still further object is to provide an external cap for the rectifier anode connections and/or base connections in which cap are located protective resistors, only safe terminals of the rectifier element or elements being exposed; also, to

enclose such protective resistors within the rectifier envelope itself.

Another object of the invention is to provide a safety cable for connections to and from the rectifier.

Still another object is to tial power supply in ous high potential tective casing.

Other ancillary objects will hereinafter appear.

In the operation of the apparatus, the novel rectifier including socket terminals, anode and cathode protective resistors, and rectifier filament heating transformer are 'designed to be conned in a metal Vhousing or junction boit preferably grounded, or they may ice located in a heavily in sulated housing of plastic or some such material, with outlets in the junction box for the connesm tions of a novel safety cable.

Alternatively, the anode and cathode protecI tive resistors may be located in a glass, plastic, or other insulated housing fused or cemented to the top and/or bottom oi the rectler, or mounted within the rectifier itself.

The nature ci the invention, however, will best be understood when descritte@ in connection with the accompanying drawings, in which:

Fig. i, is a diagrammatic view illustrating the circuit connections and arrangement of the novel rectifier unit with relation to other units oil .provide a high potenfa which the wiring of the variapparatus is confined in a pro safety hisiifvoltage power supply for operation of a cathode ray tithe.

Fig. 2 is plan view of the novel rectifier unit as installed between a safety highmvoltage trans :Former unit and a safety highmvoltage condenser unit, with safety cables between these latter and the rectifier junction box, the rectier power unit energizing the elements of a cathode ray tube through said condenser unit.

Fig. 3 is a crosssectien, on an enlarged scale, of the novel safety concentric cable for connecting the rectifier unit with other power units.

Fig. 4 is an enlarged longitudinal section, part- 1y in elevation, of Aa safety cable terminal with jacks receiving corresponding prongs.

Fig. 5 is a fragmentary view, in part section, ilustrating an alternative form of connecting cables.

Fig. 6 is a view in elevation of one form of rectifier suited tp the novel rectifier unit; and Fig. 7 is a bottom view thereofl showing its connecting prongs.

Fig. 8 1s a front elevation and part longitudinal section of an alternative form of rectifier having a special safety anode cap.

Fig. 9 is a similar view illustrating a modification.

Fig. 10 is abottom view, and Fig. 11 is a vertical section of the safety socket for receiving the base I prongs of the form of rectifier shownin Fig. 8.

Referring to the drawings, more particularly to Fig. l, I3 designates a casing or housing which may, for example, be of metal grounded at il, and is provided with an inlet preferably in the form of a suitable connecting plug (indicated in Fig. 2) which, in turn, is connected to a source of power. This source may, for convenience, be 110voit, 60-cycle alternating current, as indicated at i2, and energizes the primary I3 of a high-voltage transformer, of the magnetic leakage type, if desired, and having also a core I4 and high potential secondary |5. One terminal of the secondary of this transformer is grounded, preferably through a plurality of branches each provided with a protective resistor The lead from the other terminal is divided into a plurality of branches, in the present instance four, each with protective resistor as the respective resistors I3, i1, I3, and |9 connecting exteriorly of the casing I3 with test terminals 23, 2|, 22, and 23, respectively, which latter may also serve for connections to a rectifier unit as hereinafter set forth, or they may be extensions of a cable socket terminal.

Additional terminals 24 and 25 are provided exteriorly of the casing for power leads connected to the 110-volt supply line and running from the transformer casing as the leads 23, 21 along with the high voltage leads 23, 29, 33, and 3|, to the rectifier junction box 32 which may be of metal and grounded at 33.

The rectifier socket`34 in said junction box contains protective resistors 35, 33, 31, and 33 which are confined therein in series with the respective anode branch leads 23, 23, 33, and 3| connected to respective jacks `9, 43, 4|, and 42 of the socket.

Pin jacks 43 and 44 are also provided in the socket for the cathode heater connections for the rectifier cathode, while 45, 43, 41, and 43 designate therectiiier cathode pin jacks of said socket which are connected with protective resistors 49, 53, 5I, and 52 inserted in series in the leads 53, 54, 55, and 53 from the said respective pin jacks 45, 43, 41, and 43. Leads 51 and 53 are connected to the output of a low-voltage transformer 59 for energizing the heater of the cathode of the cathode ray tube, the transformer and conductors being placed for safety in the rectifier box 32. A low-voltage heater transformer 33 is also provided therein for safety purposes, its secondary being adapted for connection to the rectifier filament terminals through the pin Jacks 43 and 44.

Test terminals for the input leads 53, 54, 55, and 33, respectively, to the safety condenser box 6| are located exteriorly thereof as at 62, 63, 34, and 35, and protective resistors 33, 61, 33, and 63 are provided in the input leads between these terminals and the safety filter condenser unit comprising condensers 13 and 1| also housed in the metal casing or box 3| which is grounded at 12. A filter resistor 13 and protective resistors 14 for test terminals 15 and 1-3 are connected with said condensers, while protective resistors 11, 13, 19, and 33 are provided in the corresponding output branches of the filter condenser unit, as set forth in my aforesaid pendirg application Serial No. 517,336.

Test terminals 3|, 32, 33, and 34 are provided for theoutput leads of the safety condenser unit.

and test terminals 35 and 33 for the cathode ray tube heater leads are similarly provided exteriorly of the box 3|.

The cathode 31 of the cathode ray tube 33, which is energized from the condenser unit, has a negatively biased control grid 33 with video amplifier terminal 39', and is associated with a first anode 93,v having a voltage control potentiometer 93', and with a second anode 9|. Respective horizontal and vertical defiectors 92 and 93 of the tube are connected with the signal input leads 34, 95 and 93, 91 which are preferably of the shielded type.

The novel safety cable structure is shown in Fig. 3, 93 indicating the grounded outer tubular sheathing or armor of the safety cable which sheathing, as well as the shielded conductors, may be of flexible woven-wire tubing. A layer of suitable insulation 99 is included between the outside sheathing 93 and the next concentric conductor tubing |33 which may, for example, be one of the rectifier tube, high-potential anode leads such as the lead 23, Fig. 1.

A further layer of insulation |3|, such as varnished cambric, is interposed between this conductor and the next concentric conducting sheathing |32 which may be a slightly smaller flexible woven-wire tubing grounded at one end.

The next tubing of insulation |33 is included between the grounded sheathing |32 and the next conductor |34 which may be another of the rectifier anode leads as the lead 29, Fig. 1.

The remaining rectifier anode leads 33 and 3| may be located similarly and concentrically with intermediate insulation and grounded sheathing, the final and central core conductor being rectifier anode lead 3|.

If. desired, the rectifier heater transformer leads 26, 21, Fig. 1, may also be included in the same cable, with additional insulation between them and the other leads, as is well understood. The

4 connections between the rectifier cathode and the safety condenser and the connections between the safety condenser and the cathode ray tube may be made up into a similar safety cable, terminating in connecting plugs or Jacks, as indicated in Fig. 2 and hereinafter more fully set forth.

An alternative arrangement, Fig. 5, shows a variation in the manner of inserting the protected grounded. sheathing between any two live conductors and consists in providing a single conductor and grounded sheath cable, as shown at |35, for each of the rectifier anode leads instead of laying the conductors one inside the other. For example, cables for the leads 23, 23, 3|), and 3 I, Fig. 1, and similar cables for the heater transformer leads 26, 21, if desired, are laid side by side. These single cables may then be grouped in a single twisted cable or they may be laid parallel, as shown. The main requirement is that a grounded sheath |35 shall surround, each conductor suitably insulated therefrom when the cable is used for high power. For lov.r power, the interposed grounded sheathing may be omitted if desired, and only the usual insulation interposed between the high voltage conductors.

The reason for the use of the grounded sheathing in high power cables is that, in oase of a breakdown of insulation and a consequent destruction of this insulation with possible fusing of conductors, there will always be a grounded conductor between any two live conductors, so that should accidental contact by the body with a broken-down cable occur, no harm will result asomar muslin saturated with oil, in which case the cable is provided with an yoil-tight jacket.

Any other live conductors, insulating tubings, and grounded conductors of the cable may be similarly arranged in concentric form. It is to be understood that heavy insulation is required only between live conductors and grounded sheathing. As all high voltage conductors of a group are of the same potential, it is not necessary to provide anything but air or oil space between them when they are located close together as cable jack terminals.

in a metal box This casing has for convenience, surface of the casing, for example at the top.

Test terminals |3| of the safety filter condenser and test terminals`|32 of the cathode ray tube heater supply may, for convenience, and by 'lhe safety cable shown in Fig. 3 may be fanned out at its terminals as indicated inFig. 4, and the terminal block or plug |06 with the cooperating prongs |01' may be of plastic or porcelain suitable for the voltage employed. 'I'his block may be mounted in a junction box |08 similar to the box 32, shown in Fig. l, and is provided with a row of the pins or plugs |01. These are circular-ly mounted inside the box and countersunk below the surface. It will be noted that one of these pins or plugs is preferably made longer than the others. This is to make it impossible to touch more than one pin at a time accidentally, and in case of contact with such longer pin, an instinctive warning is given to proceed cautiously.

The entrance opening for the cable plug in such case is to be made smaller than the human finger. The cooperating cable terminal plug |09 may be constructed of' insulating material such as plastic with countersunk jacks |01 and the sheaths of all' cable leads entering the box are grounded as indicated. The cable connections may be either male or female, but it is preferred to have the terminals of the female type when exposed to contact with the body, as this type is less likely to present a plurality of exposed conductors which m ght be simultaneously contacted.

The general arrangement of the various` ap'- paratus hereinbefore described is indicated in Fig. 2 wherein ||0 indicates the exterior of a casing or housing which may, for example, be of metal grounded at and is provided with an inlet for a plug ||2 with leads for introducing the power from a ||0volt alternating current source of supply. vided on the outside of the casing and may be of the usual pin-jack variety, without inserted protective resistance since the supply voltage is not dangerous. Similar test terminals 24 25'y and 20,' 2|', 22', 23 for the power leads and for anode leads may also be provided. At ||6 is shown the cable plug connection of the safety cable ||1, which is grounded, and ||8 the cable plug connection to the rectifier junction box ||9 which may also be of metal, grounded at |20. Box ||9 is provided with a socket |2| of insulating materia1 such a-s porcelain or plastic and, preferably, of the wafer-type with four socket terminals |22 for connection to the rectifier anode and four socket terminals |23 for connection to the rectifier cathode. Rectifier heater socket terminals or pin jacks |24 are also included in the socket |2 An outlet plug |25 of the rectifier junction box is connected to the grounded safety cable |26, which carries an inlet plug |21 for connection to the safety condenser unit housed, for example,

Test terminals ||5 are procorrespondingl leads run through the condenser casing, be provided on the top of said casing in order to simplify cable test connections thereto. Test terminals |33 to the branch circuits from the various output protective resistors of the condenser also are provided on the top of said casing. A grounded output plug connection |34 with grounded safety cable |35 connects through a plug |36 the condenser power unit to the cathode ray tube socket terminal box |31, which may be oi' plastic, for example. The cathode ray tube |38 may be such as might beused, for example, in a television set, |39 designating the control grid lead to the video amplifier (not shown), while |40, IM designate the horizontal deflector terminals and |42, |03 the .vertical defiector ter minals or leads, all of which latter are preferably flexible and need not be heavily insulated since, by the arrangement of circuits hereinbefore described, they are safe to touch.

A suitable rectifier for use in the rectifying unit is shown in Fig. 6, wherein |50 designates the glass envelope of a low-power. high-voltage rectifier having the cathode |5|, the anode |52, the heater |53, a plurality of anode pins |54, a plurality of cathode pins |55, and the two heater pins |56. The number of anode and,V cathode pins conforms to the number of branch circuits associated therewith, and as indicated more particularly in Fig. 7, the four anode-pins |54 are connected together, and likewise the four cathode pins |55. The independently connected heater pins |56 are located between said groups of cathode and anode pins. Such rectifier istherefore adapted for use in thesocket 34, Fig. 1, and since no bodily contact is pos-sible with the cooperating jacks when the rectifier is positioned in the said socket, the rectifier circuits are perfectly safe. Withdrawing the rectifier interrupts the power connection to said rectier, and as the branch circuits of the socket terminals are each equipped with the protective resistors, the jacks are individually safe to contact.

Another form of rectifier is illustrated in Fig. 8. wherein |6| designates the glass envelope of a high-voltage, high-power rectifier having the anode |62, cathode |63, and heater |64. In the insulation base are provided two heater pins |65 and a plurality of cathode pins |66, in the embodiment shown, four, for effecting connection with suitable sources of power, all of the said cathode pins being electrically interconnected within the said base of the rectifier.

In this embodiment, the cathode and anode pins are mounted respectively at opposite ends of the envelope, and in accordance with the invention, protective resistors |61, |68, |69 and |10 for the anode are included inside a hollow anode cap |1|, mounted on top of the envelope |6|, said resistors being located in branches from the anode lead |12 to the respective cap pins |13, |14, |15, and |16. The cathode pins |66, as well as the heater pins |65, are designed to iit a special form of socket |80, Figs. 10 and 11, of insulation material, having the jacks |8| to receive the former pins and jacks |02 to receive the latter pins. Protective resistors |83 are included in leads to the respective jacks 8| and are located in said may be countersunk inthe outer f base. By eliminating the nections from jacks IBI, a socket of suitable for effecting external connection at the top of the rectifier.

In Fig. 9, a similar pin arrangement is indicated, the same being supported by a hollow socket |90 of plastic or porcelain, being four cathode pins I9I affixed thereto, together with two heater pins |92. The respective protective resistors |93, however, are in this instance mounted inside the envelope |90 of the rectifier ,and the leads united therein to form a common lead I95 which is connected to the cathode i9. Similarly, the plurality of anode resistors 200 are located within and united for connection to the anode within the envelope |94, being connected to respective pins 202 retained by an in* sulation cap 203. Over these pins may be fitted a connecting plug 204 bearing the jacks 205 from which extend the branch leads 206.

In the latter embodiment, wherein the cathode resistors are contained within the rectifier envelope, it will, of course, be appreciated that no socket resistors need be provided in the socket member adapted to receive the said cathode pins of the rectifier.

The various sockets for receiving the different types of rectiers may be mounted on the outside of a casing such as that shown at I I9, Fig. 2, with the-filament or heater transformer for a rectifier also housed in the casing. Unless the heater transformer is thus enclosed or protected, it may be subject to a breakdown between the cathode element and the heater element especially in the case of very high voltage rectifiers, thereby making the heater transformer unsafe to touch. It is therefore preferable to leave exposed only the socket terminals of the rectifier cathode with protective resistors in series.

As an example of the resistance values of, say,

resistors in the conlfour cathode protective resistors, these may be of the order of 120,000 ohms each when the transformer voltage is approximately 3,000 volts. The four protective resistors in the rectifier anode may likewise be of the same value. This places all of the four cathode or anode resistors in parallel, making a total resistance of 30,000 ohms in the cathode lead. Since the anode and cathode resistors are in series parallel, a total resistance of 60,000 ohms plus the resistance of the rectifier itself. is located between the transformer output terminals 20, 2|, 22, and 23 andthe condenser input terminals B2, 63, E4, and 65.

The transformer protective resistors I6, I1, I8, and I9, Fig. 1, of like resistivity, should have a total resistance value preferably less than that of the resistors of the rectifier, and the condenser protective resistors i6, 61, 60, and 69 should have a total resistance value greater than thatof the resistors of the rectifier.

As examples of the resistance values of the transformer protective resistors IB, I1, I8, and I9, these may be 80,000 ohms each, which is less than the resistance of the rectifier resistors; and the condenser resistors 66, 61, 68, and I59 may be 160.000 ohms, which is greater than the resistance of the rectifier resistors. Thus, each transformer resistor permits amaximum current of only 3.75 milliamperes to flow, while each rectifier resistor permits a maximum of but 2.5 milliamperes, and each condenser resistor but 1.25 milliamperes to flow.

In other words, the protective resistance values of the system should increase progressively from the high voltage source to the cathode ray tube 'this type is` acconti terminals. A convenient rule to follow in designing the protective resistors 'to avoid draining the iilter system is to increase progressively the total resistance value of each set of parallel resistors, starting with the transformer output and terminating at the filter condenser output, the number of resistors in parallel being the same for each set of resistors. Alternatively, the rule may be to decrease progressively the number of resistors of a set in parallel, all individual resistors being of the same value.

The resistance value of each resistor is such that its exposed terminals, which should be countersunk deeply below the outer surface of the casing, may be safely and comfortably contacted singly, which is 'the usual accidental contact by the human body.

Under these same conditions, a total maximum current of 15 milliamperes may flow through the transformer resistors, 10 milliamperes through the rectifier resistors, and '7.5 milliamperes through the condenser resistors. All these current values approximate the safety limit, andV while they may not be considered dangerous, they are certain to produce painful ef iects. The only way that these currents could be drawn through the body, however, would be to contact all four resistor terminals simultaneously. As this would be considerable of a feat, it would not be done accidentally, and the safety feature becomes at once apparent.

In the first place, a test probe or some such instrument is needed, to make contact with any test terminal, as these are all deeply countersunk below the surface of the casing. Secondly, upon accidental contact with any single test terminal or lead, a let go warning is given in the nature of a mild shock which immediately and instinctively warns the person contacting a live terminal to proceed cautiously.

The parallel resistor value of the protective resistors should be sufficiently low to allow optimum operation of the apparatus, but the individual resistance of each protective resistor should be suiiiciently high to produce a drop of voltage when contacted by the body to a value which is not only safe but comfortable to touch. It will be seen that any degree of safety or comfort may be obtained by simply increasing or decreasing the value of each individual protective resistor and increasing or decreasing the number of resistors in arallel in the input and output circuits of the uni s.

The type of rectifier shown in Fig. 6 is suitable for voltages up to' 1,500 volts and because of its simplicity is to be recommended. However, en larging the base diameter permits, of using higher voltages.

It will be noted, reference being had to Figs. 6 and 7, that the base pins of the rectifier shown therein are divided into groups of four each for the anode and cathode, and two for the heater.

' The reason for this is to provide an additional safety feature for the socket 34, shown in Fig. l. When the rectier is inserted in the socket, neither the anode nor `the cathode circuits can ordinarily be safely touched unless protective resistors have been included in the circuit. When the rectifier is removed, for example for testing purposes, the pin jacks 45, 46, 41, and 48 of the `cathode, and pin jacks 39, t0, 4I, and 42 of the anode, Fig. 1, are all completely separate, being made so by the removal of the connecting pins |55 and |54 of the tube base.

The high-power rectifier shown in Figs. 8 and 9 is suitable for voltages of 1,500 to 10,000 and over. It is to be understood that the protective resistors in the glass or plastic anode cap, Fig. 8, and in the base. and cap, Fig. 9, are not limited tofour. Any number may be used depending upon the current required. The same holds true for the cathode resistors .|83 in the socket member for the rectifier shown in Fig. 8. l

It is desirable, but not necessary, that the number and resistance value of protective resistors of the anode should match those of the cathode.

The arrangement described herein of highvoltage rectifier unit with the safety transformer unit and the safety condenser unit, forms a compact and moisture-proof combination, particularly suited for the operation and testing of cathode ray apparatus, such as radar oscillographs, especially when used indamp or humid climates.

I claim:

l. In a thermionic rectifier for operation at nominally dangerous current and Voltage values and including an envelope with a single anodic element and a single associated cathodic element i mounted therein: a plurality of terminals for one of the elements, separateA circuits connecting the respective terminals'to said one of the elements, and enclosed current-limiting means connected between said one of the elements and the terminals and included in series with each of said separate circuits, said current-limiting means being of an order of magnitude sufiicientiy low to permit optimum operation of the rectifier at the rated voltage and sufficiently high,'with respect to said voltage, such that upon establishment of a closed circuit between a terminal and the human body the flow of current therethrough will be limited to a harmless value due to the resultant voltage drop.

2. The thermionic rectifier of claim 1, wherein the element connected to the plurality of terminals is the anodic element.

3. The thermionic rectifier of claim 1, wherein the element connected to the plurality of terminals is the cathodic element.

4. The thermionic rectifier of claim 1, wherein respective groups of terminals and corresponding separate circuits, each with current-limiting means, are connected to the anodic element and to the cathodic element.

5. The thermionic rectifier of claim l, wherein the current-limiting means are resistors.

6. The thermionic rectifier of claim 1, wherein the current-limiting means are resistors and all of the resistors are of substantially like resistivity.

7. A thermionic rectifier having a-single anodic element and a single associated cathodic element, a plurality of terminals for one of the elements, and separate circuits connectingthe respective terminals to said one of the elements, together with enclosed respective resistors connected between said one of the elements and the terminals and included in series in each of said separate circuits.

8. The thermionic rectifier of claim 1, wherein the terminal connections comprise a fixed portion and a portion secured to the rectifier, said portions being separable from each other, and the current-limiting means are located in series with the respective fixed portions of the terminal connections.

9. In a thermionic rectifier for operation at nominally dangerous current and voltage values and including an envelope with a single anodic element and a single associated cathodic element mounted therein, a plurality of terminals for one -of theelements located exteriorly the said envelope, separate circuits connecting the respective terminals to saidhone of the elements, andenclosed current-limiting means connected between said one of the elements and the terminals and included in series with each of said separate circuits, said current-limiting means being of an order of magnitude sumciently low to permit opti mum operation of the rectifier atV the rated voltage and suficiently high, with respect to said voltage, such that uponrestablishment of a closed circuit between `a terminal and the human body the flow of current therethrough will be limited to'a harmless value due to the resultant voltage drop.

10. The thermionic rectifier of claim 9, wherein the current-limiting means are located within the envelope.

11. The thermionic rectifier of claim 9, wherein the current-limiting means are located exteriorly of the envelope.

12. The thermionic rectifier of claim 9, wherein a hollow cap is provided `over the envelope for supporting the terminals of said one of the elements and the current-limiting means are located within said cap.

13. A thermionic rectifier including an envelope with a single anode and a single associated cathode mounted therein; a plurality of terminals supported at one end of the envelope connected with the anode, and a plurality of terminals supported at the opposte end of the envelope connected with the cathode, and casings for. enclosing the respective sets of terminals.

14. The thermionic rectifier of claim l, wherein separate circuits are connected to the other element of the rectifier and are similarly provided with current-limiting means, the two with a single anodic element, a single associated cathodic element and a heater member mounted therein, a low voltage transformer mounted in the casing and adapted for connection with the rectifier hea-ter member, a high voltage source of power including a plurality of separate circuits adapted for connection with one of the said rectifier elements, a terminal member mounted in the casing for affording connection externally thereof, said terminal member being connected to the said low voltage transformer and to said high voltage source of power, and including a plurality of high voltage terminals for one of the rectifier elements separately connected to said respective circuits of the high voltage source of power, and a low voltage terminal for the heater member connected to the low voltage transformer, all of said high voltage terminals being adapted for connection with one of the rectifier elements and the low voltage terminal to the heater mem-ber, and current-limiting means connected within the casing between said one of the rectifier elements and the high voltage terminals and included in series with each of said high voltage separate circuits, said current-limiting means being of an tal energy from scid source et c viewer-cus voltege to one ci the elements W @iii/mairie" it into a plurality of independent j is, reetrictmi; the current flow in each path 't miie velue, reccm taining at seid one element l :individuel currents of the respective pettine tc @militie current ci the desired operating "velue, distributing the energy from the other eleiiieni: ci time rectifier by riiviriint,r et seid ether element the current into a. plurality ci' independent iiseiui und restricting the individual in the respective useful paths tc c. ssi-fe velue.

Uf. GAGE.

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